The present invention relates to the preparation of aliphatic carboxylic acids by the catalytic dehydrogenation of primary alcohols.
The preparation of carboxylic acids and salts of carboxylic acids using the corresponding primary alcohol as the starting material is often advantageous because the corresponding alcohols are often available and relatively inexpensive. The preparation of aliphatic carboxylic acids and their salts that possess oxygen, nitrogen and/or phosphorus heteroatoms, such as glycine, N-methylglycine, N-phosphonomethylglycine, iminodiacetic acid, N-phosphonomethyliminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid, diglycolic acid, methoxyacetic acid, lactic acid, and the like, by such means is especially advantageous. These acids and their salts are valuable, for example, as intermediates for agricultural products and pharmaceuticals, as chelating agents, as animal feed additives, etc. Conversions of primary alcohols to their corresponding acids or to salts thereof have been carried out in the art by treatment of primary alcohols with a copper catalyst under conditions that lead to either dehydrogenation (U.S. Pat. Nos. 4,782,183, 5,220,054, 5,220,055, 5,292,936, 5,627,125, 5,689,000) or oxidation (U.S. Pat. No. 5,225,592). Hydrogen is produced as a by-product in the dehydrogenation processes and water is produced as a by-product in the oxidation processes. Raney copper has typically been used as the catalyst.
Catalysts comprising cobalt, copper, and a third metal selected from iron, zinc, and zirconium and mixtures thereof, which can be made by reducing mixtures the corresponding metal oxides with hydrogen, are known from U.S. Pat. No. 4,153,581. These catalysts were disclosed in the art to be useful for the conversion of alcohols, aldehydes, and ketones to amines.
The discovery of improved processes and catalysts for converting primary aliphatic alcohols to carboxylic acids or their salts would be highly desirable.